Last summer my '01 2500HD 6.0/4L80E developed a slight trans fluid leak. Along with this a 40-50 mph vibration developed. I think there is a loose u-joint. I bought a gasket for in-between the adapter and t-case and went to install it yesterday and found a huge crack almost all the way around the adapter. I could move the t case up and down with the crack. I have read some older posts about replacing this adapter and everyone says to take the trans out to do this. Is this only a concern on the Allisons? I see no reason to need to do this. It looks very straight forward. Any advise? I was going to look for a new adapter tomorrow. Thanks

Last summer my '01 2500HD 6.0/4L80E developed a slight trans fluid leak. Along with this a 40-50 mph vibration developed. I think there is a loose u-joint. I bought a gasket for in-between the adapter and t-case and went to install it yesterday and found a huge crack almost all the way around the adapter. I could move the t case up and down with the crack. I have read some older posts about replacing this adapter and everyone says to take the trans out to do this. Is this only a concern on the Allisons? I see no reason to need to do this. It looks very straight forward. Any advise? I was going to look for a new adapter tomorrow. Thanks

You do not need to pull the trans, you need the special socket to fit the 4wd nut on the tail shaft of the transmission. (No a dana 44 axle nut socket won't work)

There is no nut on the back of the trans, just the stub shaft going to the transfer case. I have taken it apart and it was as easy as taking the bolts/nuts that mount it to each piece and pulling it off, just dont know if there was something I missed as some had said somehting about needing to disassemble the rear half of the trans to get to a lost part. Everything seems to be straight forward, just dont need any suprises.

No point in fixing it if you dont replace the bad u-joint that caused the failure. Driveshaft is out and there is no better time. Easy fix but expensive.

Yep, picking up the u-joint today. The one closest to the t-case was out (stuck) I put the new adapter in last night and threw the t-case on the shoulder and put it in. Figured I'd change the trans fuid and filter while that PITA crossmember wasnt in the way of the rear bolts in the pan.